In the prior art practice, when a tape recorder of a cassette type or open reel type is to be constructed for automation of a record, playback, stop, rewind or other operation, an electromagnetic plunger is used as a drive source to permit a "feather-touch" operation or a remote control. When a record/playback mode of the tape recorder is to be established, it is necessary to slide a head mount on which various heads, pinch roller and the like are mounted, to a record/playback position against the action of a return spring or the like and to urge the pinch roller against the capstan with a force of a magnitude which is usually on the order of 1 to 2 Kg. While the magnitude of the force varies with the variety and the size of the tape recorders, a required minimum value for apparatus of a reduced size will be on the order of 1 Kg. The electromagnetic plunger which is used to produce such force will be oversized as compared with that of the heads, occupying a greater proportion of the space on the chassis. In addition, the power dissipation is increased, which is disadvantageous from the standpoint of minimizing the overall power consumption. In addition, the use of the electromagnetic plunger causes impacts and noises when it is energized, further contributing to the generation of heat. The situation is not limited to the operation of the plunger which is used to establish a record/playback mode, but the same applies to the operation of another electromagnetic plunger which is used to establish a rewind or rapid advance mode.
In an attempt to eliminate the disadvantage from the tape recorder using such an electromagnetic plunger, a construction utilizing a combination of an electromagnet and a spring has been proposed. In particular, the magnetic attraction of the electromagnet displaces an armature against the biasing force of a return spring to change the operation mode of the tape recorder. That is, this construction utilizes a portion of the force of a drive motor which is the driving source of the tape recorder to change it into a selected operation mode. However, the control device incorporating the combination of the electromagnet and the spring has problems as follows.
First, the electromagnet must be able to displace the armature against the biasing force of the return spring by its attraction, and therefore a large-sized electromagnet is necessarily required. Secondly, the return spring must exert a force sufficient to withdraw such armature that is attracted to the magnet due to residual magnetism from the magnet and to restore it to its original position with certainty, thus a strong spring is also needed. This prior art construction was merely able to prevent generation of noise when mode changeover operation is effected, and almost no contributions have been made by it to miniaturization of the device, prevention of heat generation and decrease in power consumed.
In addition, in case of a tape recorder which is supplied with electrical power from commercial power, when the supply of power ceases as by electrical power failure while the tape recorder is in use, drive motor, that is driving source of the tape recorder, itself stops. Consequently, the tape recorder as well as a tape installed in it stops without being set in position, and this mechanically undesirable state is maintained.